Contemporary xerographic copiers often employ so-called patch sensing techniques for monitoring the level of toner in the developer. These systems establish a test pattern by discharging the photoconductor everywhere except in a discrete path or stripe and thereafter monitoring the light reflectivity of both the cleaned photoconductor and the patch. Such patches are either placed in the area of the photoconductor outside of the image areas so as not to delay copying operations or are performed by a special cycle to establish the patch in the image area and to test its reflectivity. An unsatisfactory light reflectivity of the patch area causes a response in the form of increased toner introduction or replenishment from a reservoir to a developer sump. A system for performing such an operation is shown in U.S. Pat. No. 4,178,095 by J. R. Champion and S. D. Seigal which issued on Dec. 11, 1979 and is assigned to the same assignee as the present application.
Another process for monitoring machine operation is suggested in the IBM Technical Disclosure Bulletin of January 1980 (Vol. 22 No. 8B) at pages 3606-3608 in the article entitled "Copier Adjustment" by B. A. Nilsson. This article suggests controlled introduction of gray to white transition bands on a copier during servicing so that the servicing user can compare these bands as transferred and fused on a copy sheet against a standard for a satisfactorily operating machine. The service person can then make appropriate adjustments based upon the result.
However, the prior art has not suggested that the operation of a copier is monitorable by establishing a series of light to dark transition bands on the photoconductor upon initialization of the machine, and subsequently comparing toned patches from the photoconductor with those bands so as to dynamically determine the status and appropriate responses to the machine operation.